Reducing Mind and Matter to Neutral Entities

One of the ways in which the reduction of mind to matter is pursued
proceeds in two steps. First, an analysis of mental state concepts in
terms of functional roles. Second, the identification of mental states
with those physical states that are empirically discovered to occupy
the functional roles described in the first
step.[S1]

Traditional neutral monism can be viewed as engaged in a similar, but
more ambitious, reductive project. The goal is to reduce mind
and matter to something that is neither mental nor physical.
The three traditional neutral monists conceive of mind and matter in
functional
terms.[S2]
Not the substance of which it is composed, but the role it plays,
determines the nature of a given type of thing. James’s
notorious denial of consciousness (James 1904b) applies only to
consciousness understood as some sort of “aboriginal stuff or
quality of being”. But he “insist[s] most emphatically
that it [the word ‘consciousness’] does stand for a
function” (James 1904b, 3). And Russell’s remarks about
electrons are marked by the same functionalist spirit, this time
applied to matter:

We know it [the electron] only as a hypothetical entity fulfilling
certain theoretical purposes. So far as theoretical physics is
concerned, anything that fulfills these purposes can be taken to
be the electron. It may be simple or complex; and, if
complex, it may be built out of any components that allow the
resultant structure to have the requisite properties. (Russell 1959:
22–23)[S3]

But thinking about the mental and the physical in terms of function
does raise a further question about “stuff”: something,
some stuff, must function in the relevant ways. What are the occupants
of the functional roles in terms of which mental and physical concepts
are defined? The neutral monists answer that groups of neutral
entities, appropriately interrelated, play these functional roles. And
that is to say that these groups of neutral entities are the
things to which mental and physical concepts apply. In this way the
neutral monists aim to perform a functionalist role-occupant reduction
of the mental and the physical to the neutral.

The proposal to read the traditional neutral monists are role-occupant
reductionists is debatable. None of the traditional neutral monists
frame their project in these terms. But the ideas that underlie this
form of reduction are present in the thought of all of them. The model
fits the ideas of Mach and James particularly well. And while the
model captures much of the spirit of Russell’s thought, it will
be seen (see section
4.3.1)
that certain aspects of Russell’s method of logical
construction cannot be accommodated in this framework. The most
striking difference between Russell’s constructionism and the
model of role occupant reduction presented here is this: though
Russell does pick out—via the method of logical
construction—complex structures of neutral entities that play
the relevant mental and physical roles, he refrains from identifying
these structures with the mental and physical entities that were
supposed to play these functional roles. Those entities may or may not
exist. He takes no stand on this question. All that matters to Russell
is that there is a set of entities—the logically constructed
entities—that play the relevant mental and physical roles.
Whether there are, in addition, mental and physical entities, as
traditionally conceived, we cannot tell.